The present invention generally relates to a memory device, and more particularly, to an optical memory device for recording, reproducing, or erasing information by applying an optical beam such as a laser beam or the like onto a recording medium.
A magneto-optic disc memory device which is one of optical memory devices, is a device for recording, reproducing, or erasing information by applying a laser beam onto a recording medium of a magnetic film having an axis of easy magnetization in a direction perpendicular to its surface. A method for recording or reproducing the information in the aforementioned magneto-optic disc memory device will be described below with reference to FIGS. 1, 2 and 3.
In case of recording, when the laser beam is initially modulated at strength in accordance with a recording signal after having been converged to a diameter of approximately 1 .mu.m and is applied onto the surface of the temperature of the magnetic film, the magnetic film is locally raised. Since the raised temperature of a portion of the magnetic film reduces the coercive force, when an auxiliary magnetic field is simultaneously applied thereon from outside, the information is recorded on the magnetic film through reversing of a direction to be magnetized.
In case of reproducing, the magnetic film which has been recorded on its surface is applied with a polarized straight light of the laser having a reduced amount of strength than when recording. At this moment, a polarized surface of a reflected light is inclined through a magneto-optic effect of the magnetic film called the Kerr effect. This inclination is detected by a photo-detecting element through the measuring of the strength of light, and, upon detection of this strength by a photo-detecting unit, the information is reproduced.
Generally, in the magneto-optic memory device which is recordable therein, a row of data of reproducing signals is composed of a plurality of synchronizing signal portions A each including an address portion and a sector mark indicative of a starting point of a sector, and a plurality of actual data portions B each having the information thereon, with the synchronizing signal portions A and the actual data portions B being formed in the row of data alternately with each other as shown in FIG. 1. The row of data is reproduced by an information reproducing device as shown in FIG. 2. A signal 101 initially detected by a playback head 1 is amplified through an amplifier 2 so that a reproducing signal 102 may be outputted therefrom. The signal 102 further processed in a waveform processing circuit 3 is fed into a signal detecting circuit 4 in which a digital information signal 104 is detected. The digital information signal 104 is introduced into a PLL (Phase Locked Loop) and a synchronization detecting circuit 5, and thereafter, the PLL generates a clock signal synchronized in phase on the basis of the digital information signal 104 led thereinto, while the synchronization detecting circuit 5 performs a detection of synchronization in the unit of a sector such as a sector mark.
With reference to FIG. 3, a conventional method related to a timing control for recording, reproducing or erasing will be explained below.
The synchronizing signals and the actual data of the aforementioned row of data are reproduced by the information reproducing device 7 having a construction as described above. The synchronization is detected in the synchronization detecting circuit 5 with the use of each synchronizing signal and the synchronization detecting signal 105 is fed into a timing control circuit 8 which sends timing signals 106 and 108 respectively for recording and for erasing to an information recording and/or erasing device 6 and sends a timing signal 107 for reproducing to the information reproducing device 7, on the basis of the synchronization detecting signal 105.
In the conventional method of the timing control, however, since the timing control has been performed only on the basis of the synchronization detecting signal 105, when some error has taken place on the synchronization detecting signal, the timing control cannot be correctly performed, thus resulting in a drawback that the reliability in recording, reproducing or erasing is lost.